CSS Essentials

CSS controls presentation. Understand the box model first, then use Flexbox and Grid for layout, and finish with responsive design.

Basics (Selectors & Common Properties)

Start with simple selectors, colors, spacing, and typography. Practice with small, focused snippets.

css
/* Selectors */
p { margin-bottom: 1rem; }
#highlight { background: gold; }
.note { color: #374151; }


/* Typography */
h1 { font-size: 2rem; line-height: 1.2; }
body { font-family: system-ui, -apple-system, "Segoe UI", Roboto, Arial, sans-serif; }


/* Colors, borders, radius */
.box {
  color: #111827;
  background: #f3f4f6;
  border: 1px solid #e5e7eb;
  border-radius: 8px;
  padding: 12px;
}


/* Display */
.inline { display: inline; }
.block { display: block; }
.inline-block { display: inline-block; }
Typography snippet
Box styling
Colors & Backgrounds

CSS provides multiple ways to specify colors and create beautiful backgrounds. Use modern color functions and understand different color formats for better design control.

Color Formats
Background Properties
css
/* Complete color and background example */
.color-showcase {
  /* Background with multiple layers */
  background: 
    linear-gradient(135deg, rgba(59, 130, 246, 0.1), rgba(16, 185, 129, 0.1)),
    url('/pattern.png') repeat,
    #ffffff;
  background-size: cover, 20px 20px, auto;
  
  /* Border with gradient */
  border: 3px solid;
  border-image: linear-gradient(45deg, #3b82f6, #10b981) 1;
  border-radius: 12px;
  
  /* Text styling */
  color: #1f2937;
  padding: 2rem;
  
  /* Box shadow for depth */
  box-shadow: 
    0 4px 6px -1px rgba(0, 0, 0, 0.1),
    0 2px 4px -1px rgba(0, 0, 0, 0.06);
}


/* Color scheme using CSS custom properties */
:root {
  --color-primary: #3b82f6;
  --color-secondary: #10b981;
  --color-accent: #f59e0b;
  --color-neutral-50: #f9fafb;
  --color-neutral-900: #111827;
}


.theme-aware {
  color: var(--color-neutral-900);
  background-color: var(--color-neutral-50);
  border: 2px solid var(--color-primary);
  accent-color: var(--color-accent); /* For form controls */
}
Typography & Text Styling

Typography is crucial for readability and visual hierarchy. Master font properties, text alignment, and spacing for professional-looking designs.

Font Properties
Text Alignment & Spacing
css
/* Typography scale and hierarchy */
.typography-scale {
  /* Base font settings */
  font-family: system-ui, -apple-system, 'Segoe UI', Roboto, sans-serif;
  line-height: 1.6;
  color: #1f2937;
}


/* Heading scale */
.heading-1 {
  font-size: 2.25rem;  /* 36px */
  font-weight: 800;
  line-height: 1.2;
  margin-bottom: 1rem;
  color: #111827;
}


.heading-2 {
  font-size: 1.875rem; /* 30px */
  font-weight: 700;
  line-height: 1.3;
  margin-bottom: 0.75rem;
  color: #374151;
}


.heading-3 {
  font-size: 1.5rem;   /* 24px */
  font-weight: 600;
  line-height: 1.4;
  margin-bottom: 0.5rem;
  color: #4b5563;
}


/* Body text variations */
.body-large {
  font-size: 1.125rem; /* 18px */
  line-height: 1.7;
  margin-bottom: 1rem;
}


.body-normal {
  font-size: 1rem;     /* 16px */
  line-height: 1.6;
  margin-bottom: 0.75rem;
}


.body-small {
  font-size: 0.875rem; /* 14px */
  line-height: 1.5;
  color: #6b7280;
}


/* Special text styles */
.text-highlight {
  background: linear-gradient(120deg, #fbbf24 0%, #f59e0b 100%);
  background-repeat: no-repeat;
  background-size: 100% 0.2em;
  background-position: 0 88%;
  transition: background-size 0.25s ease-in;
}


.text-highlight:hover {
  background-size: 100% 88%;
}


/* Responsive typography */
@media (min-width: 768px) {
  .heading-1 { font-size: 3rem; }
  .heading-2 { font-size: 2.25rem; }
  .heading-3 { font-size: 1.875rem; }
}
Box Model

Every element is a rectangular box made up of content, padding, border, and margin. The box-sizing property controls how width/height are calculated.

css
/* Use border-box to make sizing intuitive */
*, *::before, *::after { box-sizing: border-box; }


/* Visual spacing */
.card {
  padding: 1rem;    /* space inside */
  border: 1px solid var(--color-border);
  margin: 1rem;     /* space outside */
}
Box Model
Content (padding → border → margin)
Flexbox
1
2
3
Padding vs Margin
Border and Radius
Positioning & Layout

CSS positioning controls where elements appear on the page. Understand static, relative, absolute, fixed, and sticky positioning for precise element placement.

Position Types
Z-Index & Stacking
css
/* Advanced positioning example */
.modal-overlay {
  position: fixed;
  top: 0;
  left: 0;
  right: 0;
  bottom: 0;
  background: rgba(0, 0, 0, 0.5);
  display: flex;
  align-items: center;
  justify-content: center;
  z-index: 1000;
}


.modal {
  position: relative;
  background: white;
  border-radius: 12px;
  padding: 2rem;
  max-width: 90vw;
  max-height: 90vh;
  box-shadow: 0 25px 50px -12px rgba(0, 0, 0, 0.25);
}


.close-button {
  position: absolute;
  top: 1rem;
  right: 1rem;
  background: #f3f4f6;
  border: none;
  border-radius: 50%;
  width: 32px;
  height: 32px;
  cursor: pointer;
}


/* Sticky navigation */
.sticky-nav {
  position: sticky;
  top: 0;
  background: rgba(255, 255, 255, 0.9);
  backdrop-filter: blur(10px);
  border-bottom: 1px solid #e5e7eb;
  padding: 1rem;
  z-index: 100;
}


/* Centering techniques */
.center-absolute {
  position: absolute;
  top: 50%;
  left: 50%;
  transform: translate(-50%, -50%);
}


.center-flex {
  display: flex;
  align-items: center;
  justify-content: center;
  min-height: 200px;
}


.center-grid {
  display: grid;
  place-items: center;
  min-height: 200px;
}
Flexbox

Flexbox arranges items along a single axis with powerful alignment controls. Use it for toolbars, navbars, and one‑dimensional layouts.

css
.toolbar {
  display: flex;               /* enable flex layout */
  gap: 0.5rem;                 /* spacing between items */
  justify-content: space-between; /* main-axis alignment */
  align-items: center;         /* cross-axis alignment */
}


.item { flex: 1 } /* items can grow to fill space */
Start
Center
End
Justify Center
Wrap Rows
Grid

Grid is for two‑dimensional layouts. Define rows and columns and place items precisely.

css
.gallery {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 1rem;
}


/* Place an item to span two columns on row 1 */
.feature {
  grid-column: 1 / span 2;
  grid-row: 1;
}
1
2
3
Span 2
5
auto-fit + minmax
Named areas
Responsive Design

Use relative units, fluid containers, and media queries. Start mobile‑first, then scale up.

css
/* Mobile-first styles */


.container { max-width: 100%; padding-inline: 1rem; }


/* Enhance at larger screens */
@media (min-width: 768px) {
  .container { max-width: 60ch; margin-inline: auto; }
}


/* Modern container query example */
.card { container-type: inline-size; }


@container (min-width: 420px) {
  .card { display: grid; grid-template-columns: 1fr auto; gap: 1rem; }
}
Practical tips:
  • Design mobile-first, then add breakpoints with @media.
  • Use flexible units like fr, %, and rem.
  • Set images to max-width: 100% and height: auto.
Fluid image
Mobile-first layout